1. “Unboxing” means taking an Integer object and assigning its value to a primitive int. This is done using the.intValue( ) method. Example; Integer z = new Integer(7); // box int y = z.intValue( ); // unbox Note that we have already done this when accessing an integer that is stored in an ArrayList. (See ArrayListDemo.)

2. The.equals( ) method is in the Object class, and is overridden in both the String and Integer classes. We know how.equals( ) works with Strings. With Integer objects, it compares their values. Example: Integer a = new Integer(2); Integer b = new Integer(2); if (a.equals(b)) // true

3. .equals vs == However, with objects, == does NOT actually compare their values. Instead, it checks to see if they are aliases of each other – which means that they are both stored in the same location in the computer’s memory. What do you think the result of the following code is? Integer x = new Integer(24); Integer y = new Integer(24); System.out.println(x==y); // displays false NOTE: for reasons we won’t get into, Strings are not treated like other Objects in this situation. Both.equals and == compare their values.

4. Review: a constant is a variable that is declared using the keyword final; it is used with variables whose values can never change Example: public final double RATE = 3.06; The Integer class has 2 constants that store the maximum and minimum possible values for an Integer: Integer.MAX_VALUE // equals 2 31 -1 (about 2.1B) Integer.MIN_VALUE // equals -2 31

5. The only wrapper classes you need to know are Integer and Double. The Double class works similarly to Integer. (Although, Double.MIN_VALUE is poorly named – it actually means the minimum absolute value that a Double can be.)

6. Source Code vs. Bytecode The code you write is called source code. It is saved in a file with the extension.java. Once you compile it, it is converted into bytecode, which is saved in a file with the extension.class. A program called the Java Virtual Machine understands and runs bytecode. At the lowest level, a computer only understands Machine Language, made up of ones and zeroes. Think of bytecode as an intermediate language between source code (high-level language) and Machine Language (low-level). So, the java compiler (in our case, Jcreator) converts your source code into language that the computer can execute.